Conventionally, in a manufacturing process for a semiconductor device, an etching target film, such as a silicon oxide film or the like is plasma etched via a resist mask to have a desired pattern. As for such plasma etching method, there is known a technique for performing micro-processing with a high accuracy by using a multilayer resist mask.
In a plasma etching process using the above-mentioned multilayer resist film as a mask, there is known a plasma etching method in which an organic film serving as a lower resist film is plasma etched by using a plasma of a processing gas while using a mask of a silicon-containing film formed thereon. In the plasma etching process, a single gas of O2 gas, a gaseous mixture of O2 gas and N2 gas, a gaseous mixture of O2 gas and CO gas, and a gaseous mixture of O2 gas and CH4 gas are used as a processing gas. Further, in the plasma etching process, a gaseous mixture of O2 gas and a rare gas is also used as the processing gas (see, for instance, Japanese Patent Laid-open Application No. 2004-296991).
In the plasma etching method using the above-mentioned multilayer resist mask, the organic film is chemically etched, so that there occurs a problem that a sidewall portion of the organic film may not be etched to have a perpendicular shape. That is, the sidewall portion of the organic film may be etched excessively and curved to result in the occurrence of the so-called “bowing”, or a portion under the mask may be excessively etched, resulting in the occurrence of the so-called “undercut”.